SYSE.34:4.2 - Choose a change strategy and its states

Compare a bounded coordinated interruption with compatible coexistence. A short interruption can be simpler and safer for a small service; coexistence is useful only when its compatibility can actually be maintained. For either strategy, qualify the recovery actions available from its intermediate states, including forward repair where it is needed.

For parallel change, add the needed representation without prematurely removing the old contract, qualify coexistence, migrate consumers, and contract only after the old use has been resolved. The historical Parallel Change Method supplies that strategy, not an engine-specific synchronization mechanism.

Identify what is valid at each intermediate state: which executable can read or write, what data transformation has occurred, and what return remains possible. A failed step must have a known stop or recovery action from its actual partial state.